Each authority spent more on outside advice than the Welsh Assembly Government, which spent almost £2m on services from consultancy firms like Pricewaterhouse Coopers, Bravosolutions and Elan.

The figures were obtained under the Freedom of Information Act by the BBC Radio Wales programme, Wales at Work, broadcast last night.

The revelation has drawn criticism that the costs were eating up scarce resources, but the Welsh Local Government Association (WLGA) pointed out that councils did not always have consultants’ expertise in-house.

Conwy Council said in a statement: “Conwy is a very lean authority with the lowest council tax in North Wales and third lowest in the whole of Wales.

“We don’t have spare capacity and therefore when we need specific expert advice on capital schemes or on large flagship projects such as the new regional swimming pool or the Venue Cymru project, we buy in the expertise as and when required.

“Such expertise is generally fully funded by WAG and other grants, and much of our spend on consultants does not impact directly on our council tax payers.”

Anna Freeman, WLGA director of employment said: “The use of management consultancy is commonplace in all sectors. Local authorities are multi-million pound businesses that offer hundreds of everyday services to communities.

“However, there is a limit to the specific professional expertise that is available to them within their authority.

“The term ‘management consultants’ covers a plethora of professional and technical expertise, advice and support that can help local councils to deal with a particular issue at a given time.

“It would be very difficult and expensive for councils to permanently employ all the detailed experience and expertise they might ever need.

“The short-term use of the right management consultants can be a cost-effective alternative. Management consultants are also used to assist with statutory functions like auditing of accounts, and can provide councils with a valuable external, independent view.

“The prudent and effective use of management consultants across a wide range of local authority functions is an entirely appropriate investment in the drive towards improving public services, including increased value for money.”

Unison, the public sector union, criticised the amount of spending on outside consultants.

Paul Elliott, head of local government for Unison in Wales, said: “There’s only a certain amount of money available for public services.”